Gas effusion: read below?

In this problem where no temperature or pressure is given it must be assumed to be at STP. Therefore, if it takes 15.2s for 21.6mL of a gas to escape then it would give a leakage rate of 21.6mL/15.2s = 1.42mL/s. Divide 29.8mL by 1.42mL/s yields 20.98seconds. PROOF: 15.2s x 1.42mL/s= 21.6mL. And: 20.98s x 1.42mL/s=29.79 or 29.8mL